scripts: enable checks for unassigned uppercase (#3302)

As almost all variables are upper-case and do not follow the intention of
https://github.com/koalaman/shellcheck/issues/1037#issuecomment-341288433
include checks for unassigned upper-case variables.

scripts/container.sh

 #!/usr/bin/env bash
+# shellcheck enable=check-unassigned-uppercase
 
 set -euo pipefail
 
@@ -21,4 +22,3 @@ else
 	echo "Please install either podman or docker. Exiting" >&2
 	exit 1
 fi
-

scripts/patch.sh

 #!/bin/bash
+# shellcheck enable=check-unassigned-uppercase
 
 set -e
 shopt -s nullglob

scripts/update-modules.sh

 #!/usr/bin/env bash
+# shellcheck enable=check-unassigned-uppercase
 
 set -eo pipefail
 

scripts/update-patches.sh

 #!/bin/bash
+# shellcheck enable=check-unassigned-uppercase
 
 set -e
 shopt -s nullglob